SAN ANTONIO — Boston Celtics rookie Robert Williams missed the last two games against the Houston Rockets and Memphis Grizzlies, and he will be out Monday as well, as the Celtics take on the San Antonio Spurs.

In the locker room prior to the game, MassLive pointed out to Williams that his size would have helped on Saturday against the Grizzlies and Marc Gasol — the Celtics were also without Aron Baynes, which left only Al Horford and Daniel Theis in the normal big rotation. The point was not lost on Williams.

“Right? Right?” Williams said, smiling. “Yeah definitely, from that perspective, because s—, I just want to be out there with my teammates helping them out. It’s definitely difficult watching, not being able to be in the game.”

Williams injured himself in practice, and Stevens said the rookie would likely be day-to-day when the Celtics return to Boston. The team hasn’t given him a timeframe, and Williams said he has simply been sticking to the rehab schedule given to him by the team’s trainers.

“I definitely feel it getting better, but it’s a day-to-day process,” he said. “It’s a lot that goes into it, with each day getting all the treatment that I need, hoping that it steadily improves.”

Williams still wasn’t able to pinpoint when the injury occurred exactly.

“I don’t pay attention to my actions, so I couldn’t really pinpoint what I did,” he said. “But definitely unfortunate. But like I said, I’m on the road to recovery. …

“It’s about bringing energy, doing whatever I can do to keep these guys on their toes. That’s what I’m here for.”